The present invention relates to the general art of geotechnical engineering, and to the particular field of overfilled arch structures.
Frequently, overfilled bridges formed of precast or cast-in-place concrete are used to support one pathway over a second pathway, which can be a waterway, a traffic route or the like. The terms xe2x80x9coverfilled archxe2x80x9d or xe2x80x9coverfilled bridgexe2x80x9d will be understood from the teaching of the present disclosure, but in general, an overfilled bridge or an overfilled arch is a bridge formed of arch elements that rest on the ground or on a foundation and has soil or the like resting thereon and thereabout to support and stabilize the bridge. The arch form is generally cylindrical in circumferential shape, and in particular a prolate shape; however, other shapes can be used. An example of an overfilled bridge is disclosed in U.S. Pat. Nos. 3,482,406 and 4,458,457, the disclosures of which are incorporated herein by reference.
Presently, reinforced concrete overfilled arches are usually constructed by one of two methods. The first method includes completing the entire arch structure in place, with formwork used to create the arch profile. This method generally requires formwork on both the inside and the outside of the arch profile as the sides of the arch are generally too steep to be cast without the support provided by formwork. Formwork on the outside of the arch may generally be omitted at the apex of the arch where the gradient of the arch shell is less than about 20xc2x0 to 30xc2x0 from horizontal. The provision of such outside form work is both costly and time consuming and may reduce the finished quality of the formed concrete. Furthermore if outside formwork is used, there are restrictions on the thickness of the vault, such as to ensure good qulity concrete the arch vault cannot be less than roughly one foot thick.
A second common method of constructing reinforced concrete overfilled arches is to pre-cast the complete arch or arch halves in sections (elements) and to subsequently place the pre-cast elements onto prepared footings. An example of this type of construction method is disclosed in U.S. Pat. No. 3,482,406. This construction method requires construction of re-usable molds and the transport and lifting of the finished arch profiles into their permanent locations. The aforementioned re-usable mounds are a significant initial investment. This renders this method of construction uneconomical if the molds cannot be re-used to supply elements for the construction of many arch bridges. Investment in such molds is therefore made by pre-casting manufacturers and the arch elements are produced in their factories and transported to the bridge construction site. Problems associated with the transport of such arches and the requirement of a construction crane large enough to lift complete arch elements are disadvantages of this method.
Furthermore, transporting large pre-cast structures may involve complex and expensive transportation problems. Roadways, permits, escorts and clearance requirements must be accounted for, as well as traffic problems and schedules. Still further, in some constructions, very large cranes are required which further exacerbates all of the above-mentioned problems.
Therefore, there is a need for an economical and efficient overfilled bridge and method of constructing an overfilled bridge.
Pre-cast structures are not as versatile as possible, especially if unusual terrain or specifications are present. In particular, precast structures are limited in the forms of curtailment which can be applied at the ends of the bridge. Therefore, there is a need for an overfilled bridge and method of constructing an overfilled bridge that is versatile and amendable to design variations.
It is a main object of the present invention to provide an economical and efficient bridge structure and method of forming an arched overfilled bridge structure.
It is another object of the present invention to provide a reinforced concrete arch bridge that can be constructed completely on the construction site.
It is another object of the present invention to provide an overfilled arched bridge and method of construction therefor which incorporates small pre-cast components.
It is another object of the present invention to provide an overfilled arched bridge and method of construction therefor which is amenable to including various arch profiles and shapes.
It is another object of the present invention to provide an overfilled arched bridge and method of construction therfor which is more versatile with respect to the formable geometry at the ends of the arched bridge.
It is another object of the present invention to provide an overfilled arched bridge and method of construction therefor which is flexible and versatile and amenable to design variations.
It is another object of the present invention to provide an overfilled arched bridge and method of construction therefor which is amenable to including various arch profiles using the same formwork.
It is another object of the present invention to provide an overfilled arched bridge and method of construction therefor which reduces dependence on large element transportation.
It is another object of the present invention to provide an overfilled arched bridge and method of construction therefor which reduces initial capital investment required.
It is another object of the present invention to provide an overfilled arched bridge and method of construction therefor which is expeditious to produce.
These, and other, objects are achieved by a hybrid arched overfilled bridge structure and method for constructing the same which combines pre-cast elements with cast-in-place sections. The hybrid bridge thus realizes the advantages associated with precast elements and with cast-in-place elements while omitting most, if not all, of the disadvantages associated therewith. The pre-cast elements can be small and thus will avoid the aforediscussed transportation-related costs and problems, and the cast-in-place sections will avoid the above-discussed formwork problems. The hybrid bridge embodying the present invention thus takes advantage of both methods of construction while avoiding most, if not all, the problems associated with each of the methods of construction.
Furthermore, since the pre-cast side elements make up a shorter sector of the arch than is the case with prior bridges, it is possible to pre-cast them lying flat (that is, comparable to a curved slab) rather than vertical (comparable to a curved wall). This makes casting simpler and cheaper than prior methods and the required forms are much cheaper than the forms required by prior methods. Furthermore, as compared to prior methods of construction of overfilled bridges, it is more feasible to perform the side element casting operation locally on the construction site at which the arch is being built using the pre-cast side elements of the present invention.
Still further, the pre-cast components of the present invention are lighter, less unwieldy and easier to work with than prior elements and thus are easier to cast, stock, transport, unload and erect than prior bridge components.
Still further, since the upper part of the bridge structure (the crown sector) is cast in place, it can be continuous and thus the distribution of loads on the structure will be enhanced by shell action. Trimming the ends (battered ends) along the plane of the embankment is much simpler with the bridge structure of the present invention than with prior bridge structures where both spandral and wing walls were required. Because the crown sector of the present invention is cast in place, it will be less costly than prior bridge structures, yet will still be high quality and have a desired aesthetic appearance.